Thorough knowledge of normal craniofacial development is of great importance in beginning to understand the etiology and pathophysiology of developmental anomalies in this region. Congenital craniofacial and dentofacial malformations are very common in humans. Our long term goal is to better understand normal and abnormal embryonic craniofacial development at the molecular level and specifically to both define and understand the significance of the patterned expression of members of the syndecan family of cell surface receptors during normal and abnormal development of mandibular skeletal elements. The sequential expression of receptors for the extracellular matrix (ECM) and/or for components of the peri-cellular microenvironment, such as growth factors, may regulate or represent different levels of patterning and differentiation during embryogenesis. These concepts make the study of the syndecans, a family of transmembrane heparan sulfate proteoglycans (HSPG) of particular interest. Syndecans are known to associate with the cytoskeleton and are able to bind a broad range of molecules in the extracellular environment. Individual syndecan family members have been shown to have distinct patterns of expression during embryonic development in the mouse model. Through the specific aims listed below we will test the following hypotheses: (1) The syndecan family of cell surface proteoglycans displays spatial and temporal patterning during the embryonic development of the skeletal components of the mouse mandible. (2) The regulated expression of the syndecans plays an important functional role in the developmental transitions during development of the mandibular skeleton. (3) Agents that disrupt normal development of the mandibular skeleton disrupt the normal pattern of expression of the syndecans. This study has the following specific aims, with particular emphasis on skeletogenesis in the first branchial arch: (1) Define in detail the spatial and temporal expression patterns of the syndecans in normal mouse mandibular development, using an in-situ hybridization and immunohistochemistry in whole mouse embryos and in mouse mandibular explants at different stages in their development. The explants will be cultured in serumless, chemically defined medium as described by Slavkin. (2) Determine if these expression patterns are required for normal mouse mandibular development, by perturbing translation of the syndecans with the use of anti-sense oligodeoxynucleotides (ODNs) during explant culture. (3) Determine if agents known to disrupt normal skeletogenesis in the craniofacial complex alter the normal expression patterns of the syndecans. These agents will include anti-sense ODNs to EGF, tyrphostin, which disrupts EGFR mediated signalling and retinoic acid. These studies will determine whether regulation of syndecans and skeletogenesis are tightly linked and will form the foundation of future experiments using transgenic approaches.